Abstract
In sedimentary basins and volcanic edifices, granular materials undergo densification that results in a decrease of porosity and permeability. Understanding the link between porosity and permeability is central to predicting fluid migration in the sedimentary crust and during volcanic outgassing. Sedimentary diagenesis and volcanic welding both involve the transition of an initially granular material to a non-granular (porous to dense) rock. Scaling laws for the prediction of fluid permeability during such granular densification remain contested. Here, based on collated literature data for a range of sedimentary and volcanic rocks for which the initial material state was granular, we test theoretical scaling laws. We provide a statistical tool for predicting the evolution of the internal surface area of a system of particles during isotropic diagenesis and welding, which in turn facilitates the universal scaling of the fluid permeability of these rocks. We find agreement across a large range of measured natural permeabilities. We propose that this result will prove useful for geologists involved in modeling porosity-permeability evolution in similar settings.
Highlights
Granular materials deposited in sedimentary basins commonly densify by compaction and cementation (Fowler and Yang, 1998), and in volcanic systems by viscous processes of compaction and sintering (Quane and Russell, 2005; Wadsworth et al, 2014)
In sedimentary basins and volcanic edifices, granular materials undergo densification that results in a decrease of porosity and permeability
We provide a statistical tool for predicting the evolution of the internal surface area of a system of particles during isotropic diagenesis and welding, which in turn facilitates the universal scaling of the fluid permeability of these rocks
Summary
Granular materials deposited in sedimentary basins commonly densify by compaction and cementation (Fowler and Yang, 1998), and in volcanic systems by viscous processes of compaction and sintering (Quane and Russell, 2005; Wadsworth et al, 2014) These processes in turn significantly change the microstructure and the fluid permeability through the rocks (e.g., Bourbie and Zinszner, 1985; Heap et al, 2015). Universal scaling of fluid permeability in rocks across the granular to non-granular transition (via Equation 1) using either measured s (specific surface, ratio of internal surface area to sample volume) or, if unknown, calculated ‐evolution of s during densification (using Equations 2 and 3) showing good agreement without any fitting parameters (r 2 = 0.96) over a large range of normalized permeability [k—permeability; f—porosity; fc—percolation threshold; f* = 1 – (f – fc); fm—maximum packing porosity of particles]. In the Data Repository, we provide this scaling for other combinations of overlapping and nonoverlapping particles and pores to show that these work less effectively than the method presented here (0.56 < r2 < 0.93)
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